The papermaking process requires the individual particles of fiber and pigment, e.g., titanium dioxide, be brought together to form the sheet. The process of forming the sheet takes place by dewatering a dilute aqueous dispersion of the papermaking components (i.e., fiber and pigment). However, it is generally recognized that the surface of papermaking components have electrostatic charges. Because of the high surface to volume ratio of the papermaking components, these surface charges play a dominant role in the dewatering process and the formation of the sheet. These surface charges cause subtle interactions between the particles, and as a result, they have a direct impact on both the opacity and the formation of the decor paper. Manipulating these surface charges to enhance the quality of paper is one of the primary purposes of wet end chemistry. Various types of paper can be prepared, dependent upon the amounts of additive(s), fiber(s) and pigment(s).
Decorative laminate is a generalized term used to describe a decorative covering commonly used in the furniture and construction industry. Decorative laminates are composed of resins and paper. The resins provide a protective layer for durability and wear resistance. Decor paper is the surface sheet used to manufacture decorative laminates, it is available in a variety of solid shades and printed patterns.
Historically, decor papers were manufactured by using a combination of alum (aluminum sulfate) and sulfuric acid. Low levels of alum provide for fiber charge neutralization, reducing the fiber-fiber repulsion. The alum is thought to increase the cationicity of titanium dioxide particles present in the papermaking solution. The sulfuric acid is present to control the pH. Sulfuric acid, unlike alum, does not become incorporated in the sheet at reasonable addition levels and therefore does not contribute to sheet pH. The overall effect of using alum and sulfuric acid is improved optical properties and sheet uniformity. This result is obtained because alum provides for a more uniform dispersion of titanium dioxide and it allows the Van der Waals forces to play a more dominant role in the fiber-fiber interaction. However, this approach to manufacturing decor papers is not without limitations and flaws. Minor process variations cause the amount of sulfuric acid and alum needed in the papermaking system to vary widely. Because sulfuric acid is a strong acid, minor changes in the papermaking process lead to great changes in the system pH. Likewise, changing process conditions alter the optimum amount of alum needed for good formation and low sheet pH. Together these factors, (process variations which cause changing but unpredictable sulfuric acid and alum requirements) make it difficult to produce a consistent quality sheet useful for the production of decor sheets.
Recently, aluminum triformate (ATF, Al(O2CH)3) has been used as a replacement for both alum and sulfuric acid in decor paper manufacturing. Aluminum triformate is less acidic than alum and it does not effect the sheet pH as much as alum does. (The reduced acidity is due to the fact that formate ion coordinates with the aluminum more strongly than the sulfate ion does.) As a result of the reduced acidity, ATF can be used with success for both pH control and charge neutralization in decor paper manufacturing. ATF provides more consistent results than alum and sulfuric acid because ATF is considered to be less sensitive to process variations.
Although, aluminum triformate provides a unique benefit in the manufacture of decor paper, its use is not without complications. ATF is difficult to manufacture, and therefore it has limited availability, and it is expensive. ATF is also difficult to use because of its limited solubility and because of its facile thermal decomposition. U.S. Pat. No. 5,468,892 highlights the difficulties in preparing aluminum triformate. These authors confirm that ATF has many uses but limited availability. The Kirk Othmer Encyclopedia of Chemical Technology notes that xe2x80x9cmost commercial aluminum formate is the monobasic aluminum diformate because of the difficulties involved in aluminum triformate preparationxe2x80x9d. U.S. Pat. No. 5,468,892 confirms this by stating that ATF is only marketed as a solid or as basic aluminum formates with a considerable content of free hydroxyl groups.
Basic aluminum formates do not have the same reactivity as ATF, and are undesirable when manufacturing decor paper. U.S. Pat. No. 5,468,892 describes the preparation of solutions of ATF via reaction of sodium aluminate with formic acid. Although this approach has some utility, the reaction between the sodium aluminate and formic acid is poor and is uneconomical. Additionally, sodium aluminate contains considerable unreacted alkali. This unreacted alkali consumes formic acid in an unproductive reaction to form sodium formate. Preparation of ATF by the reaction of sodium aluminate with formic acid requires as much as a 70% excess of formic acid. The undesired reaction which consumes formic acid to produce sodium formate, substantially increases the cost of manufacturing ATF by this route. These difficulties preclude there being a readily available and economical source of ATF or ATF derivatives.
As a consequence of these disadvantages, a need therefore exists for an alternative to ATF for the manufacture of paper, and particularly, decor paper.
The present invention circumvents the problems described above by providing aluminum compounds which can be incorporated into a paper making process at a substantially lower pH than that currently available, that helps to uniformly disperse titanium dioxide in the paper product, thereby helping to increase opacity, and improves the durability of the paper. In a particular embodiment, the aluminum compounds of the invention are compounds having the formula AlX3xe2x88x92n(Y)n. Each X, independently, can be a halide, an alkoxide, a hydroxide, a nitrate, a perchlorate or combinations thereof. Each Y, independently, can be an anion of an organic acid having one to six carbon atoms and the value of n is between about 0.01 and 2.99. For example, the an anion of an organic acid can be acetic acid, hydroxy acetic acid, oxalic acid, succinic acid, citric acid, maleic acid or formic acid with n being between about 2 and 2.75. In a preferred embodiment, X is chloride, Y is formate, and n is between 2 and 2.75.
The aluminum compounds of the invention may be used in a variety of paper applications, including use in decorative laminates such as those decorative coverings commonly used in the furniture and construction industry. The aluminum compounds of the invention are also useful as pigments, catalysts, and in size manufacturing, in paper manufacturing, paint manufacturing, as well as, textile and leather processing. It is understood that the term xe2x80x9caluminum compoundxe2x80x9d encompasses any aluminum species which falls within the formula AlX3xe2x88x92n(Y)n as described herein.
The invention provides methods for the preparation of compounds having the formula AlX3xe2x88x92n(Y)n wherein each X, independently, can be a halide, an alkoxide, a hydroxide, a nitrate, a perchlorate or combinations thereof. Each Y, independently, can be ananion of an organic acid having one to six carbon atoms and the value of n is between about 0.01 and 2.99. The method includes combining between 4 moles and 5 moles of an organic acid having one to six carbon atoms acid with 1 mole of aluminum halohydrate. In preferred embodiments, the organic acid is formic acid or acetic acid and the aluminum halohydrate is polyaluminum chloride, preferably, aluminum chlorohydrate. Preferably, the method produces formic or acetic acid aluminum chlorides where n is between 2 and 2.75, preferably between 2.333 and 2.666. In a particularly preferred embodiment, the method produces an aluminum compound where X is a mixture of chloride and hydroxide and the organic acid is formic acid. Preferably the method produces formic acid aluminum compound/hydroxide/chloride mixtures where n is between 2 and, preferably between 2.333 and 2.666. The resulting product can be used in concentrated form or diluted to obtain a stable solution.
In another aspect, the present invention pertains to methods for preparing a compound having the formula AlX3xe2x88x92n(Y)n wherein each X, independently, is a halide, an alkoxide, a hydroxide, a nitrate, a perchlorate or combinations thereof. Each Y, independently, is ananion of an organic acid having one to six carbon atoms and the value of n is between about 0.01 and 2.99. The methods include combining about 4 moles of an organic acid having one to six carbon atoms acid with 1 mole of polyaluminumhalide. In one embodiment, the organic acid is formic acid and wherein polyaluminum halide is polyaluminumchloride. In a preferred embodiment, the process produces an aluminum compound where X is chloride and Y is formate. The resulting product can be used in concentrated form or diluted to obtain a stable solution.
All percentages by weight identified herein are based on the total weight of the composition unless otherwise indicated.